Method of and apparatus for heating the surface part of various construction materials



Nov. 12, 1968 MASAO ANDO 3,410,977

METHOD OF AND APPARATUS FOR HEATING THE SURFACE PART OF VARIOUSCONSTRUCTION MATERIALS Filed March 28, 1966 United States Patent "ice 3410,977 METHOD OF AND APPARATUS FOR HEATING THE SURFACE PART OF VARIOUSCONSTRUC- TION MATERIALS Masao Ando, 72 Higashi-tamagawa-cho,Setagaya-ku, Tokyo, Japan Filed Mar. 28, 1966, Ser. No. 538,040 3Claims. (Cl. 219-10.49)

ABSTRACT OF THE DISCLOSURE Method of and apparatus forheating thesurface of a road, floor and the like by using a heat-generating pipeburied in the construction material, consisting of an outside pipe madeof a highly magnetic metal and an insulated wire disposed in the insideof said outside pipe, one end of said insulated wire being connected toone terminal of an alternating current source and the other endconnected to a terminal fixed on one end of said outside pipe, the otherend of the outside pipe being directly connected to the other terminalof the alternating current source. When an alternating current flowsthrough the outside pipe, it passes only the inner surface of said pipeby the skin effect of the alternating current so as to generate heat onthe inner surface of said pipe without current appearing on the outersurface of said pipe.

This invention relates to a method of and apparatus for heating thesurface of road or Wall electrically.

Recently various electrical heating methods have been attempted to heatthe surface of road and floor in order to prevent them from beingfrozen, also to thaw snow or to heat a building.

Among them, there is known a method in which cables having insulation ofbutyl rubber and sheath of polyvinyl chloride (hereinafter it will bereferred to as BN cable) or mineral insulated cables having a sheath ofmetal (hereinafter it will be referred to as MI cable) are buried underthe road surfaces or in the inside of walls and electricity is passedtherethrough to generate heat.

Though the method relied on the BN cables is relatively inexpensivecompared with those relied on the MI cable, the BN cables are liable tobe broken. Though the MI cables possess greater mechanical strength, theconnection method thereof is rather complicated. Because of thefabrication problem, the metal sheath of the MI cable is made of thesame material with core material and for this purpose copper is mostlyused which makes the MI cables relatively expensive. Furthermore thecopper does not adapt itself well to the construction material of roadand floor, such as concrete, asphalt and the like. Hence it is liable tobe damaged when it is used under the road Where there is trafiic ofheavy vehicles.

An object of the present invention is to provide a method for heatingthe surface of road, floor or wall electrically which has overcome theabove-mentioned drawback inevitable in the conventional methods.

Another object of the present invention is to provide an apparatus whichcan heat the surface of road, floor or wall electrically with economicaladvantage.

Such objects and other advantage can be attained by the method and theapparatus of the present invention.

The apparatus of the present invention consists of an outside pipe ofhighly magnetic metal which is buried in the to-be-heated constructionmaterial and a perfectly insulated wire disposed in the inside of thesaid outside pipe. One end of said insulated wire is connected to oneterminal ofan alternating current source and the other end is connectedto a terminal fixed on one end of the said out- Patented Nov. 12, 1968side pipe, the other end of the said outside pipe being directlyconnected to the other terminal of the said alternating current sourceso as to generate heat only on the inner surface of the said outsidepipe when an alternating current is passed through the wiring system.The method of the present invention consists in generating heat on theinner surface of an outside pipe made of a highly magnetic metal andburied in the inside of a construction material by passing thealternating current only on the inner surface of the said outside pipeby using an insulated wire which is disposed in the inside of the saidoutside pipe. One end of said insulated wire is connected to analiernating current source and the other end is connected to the otherend of the said outside pipe, and the other end of the said outside pipeis directly connected to the other terminal of the same alternatingcurrent source.

A preferred embodiment of the invention has been chosen for purposes ofillustration and description and is shown in the accompanying drawings,forming a part of the specification, together with the contrast drawingusing conventional apparatus wherein FIGURE 1 shows schematically thedistribution of current and voltage in the inside of steel pipe whenalternating current is passed through the wire placed in the inside ofthe said steel pipe, FIGURE 2 shows schematically the distribution ofcurrent and voltage in the apparatus of the present invention, FIGURE 3shows the apparatus of the present invention when it is buried under thesurface of a road, corresponding to the view of the cross section takenalong the line X-Y of the FIGURE 4, and FIGURE 4 shows one embodiment ofthe method of burying the apparatus of the present invention.

In the contrast drawing, FIGURE 1, 1 is an alternating current source, 2is a steel pipe (e.g. having a thickness of about 3 mm. and 3 is aninsulated wire having a cross sectional area of about 22 mm. which ispassed through the steel pipe 2 as shown in this figure.

When an alternating voltage of commercial frequency is impressed fromthe source 1, a current flows in the wire 3. For illustration purposesthis current is i. Since 2 is a highly magnetic steel pipe, a current iwhich is approximately equal to i flows through the pipe 2 in thedirection shown in the FIGURE 1. In other words, i is an eddy currentand also a skin current. It is Well known that the depth of the skin a(cm.) can be expressed by an equation:

wherein p is a specific resistance (9 cm.) and is a permeability (0) andf is a frequency of the source. (c./sec.) Accordingly in order to makeizi', it is necessary that the thickness of the steel pipe, 2 cm. mustsatisfy the following relation.

In the circuit shown in FIGURE 1, a voltage e appears on a voltmeter 9inserted between terminals p and q and its value is approximately halfthe voltage of the source 1. When short circuit or earthing occurs,between p and q the current i varies. Accordingly this connection has aserious drawback in that a human being or animal passing this part maysustain injury.

In contrast to the connection of FIGURE 1, the apparatus of the presentinvention has a connection of FIG- URE 2. Namely the insulated wire 3from a source 1 is passed through the inside of a steel pipe andconnected to a terminal 4 conductively fixed on one end of the pipe. Theother end of the source 1 is connected to the terminal 5 fixed on theother end of the steel pipe. By such an arrangement, the current iflowing through the steel pipe exists only on the inner surface of thewall by the skin effect and does not appear on the outside of the pipe.For

3 example, even if the terminals p and q fixed on the outside of thepipe are connected to a voltmeter 9, the reading of voltage is zero andas indicated by 8 and 8' even when earthings are effected, there is noflowing of earth current.

The method for surface heating of the present invention can be reducedto practice by using the steel pipe schematically shown in FIGURE 2 asheating elements. FIGURES 3 and 4 shows the arrangement of such aheating element buried under the surface of the ground. In thesedrawings 1 is an electric source, 2 is a steel pipe, 3 is insulatedwire, 4, 5 and 6 are terminals and 8 is the earth. An alternatingcurrent from a source 1 flows to a terminal 6, through an insulated wire3 disposed in the inside of a steel pipe 2 and reaches a terminal 4,from there it passes only the surface part of the inside wall of thesteel pipe, from the terminal 5 it leaves the steel pipe and returns tothe source 1. Accordingly even when such steel pipes are buried inconcrete asphalt, conductive earth, or the like, and even when shortcircuit is made by a steel plate 7 or the like, the current i isconstant and no earth current or short circuit current flows so long asthe insulation of the wire 3 from the terminal 6 to the terminal 4 isperfect. This means that there is no voltage appearing on that part andit is not harmful to a human being, animal or the like.

Since the heating element is of steel, it adapts itself well toconcrete, asphalt or the like road, floor or wall.

Further it can be reinforced simply by structures such as steel plates 7and hence it can be of strong construction. There are further advantagesthat the temperature distribution on the surface of road, floor or wallor the like can be made uniform by using relatively broad steel plates 7and since the construction material is of steel, it is less expensiveand more economical than copper used mostly in MI cables.

What is claimed is:

1. A method for heating the surface of construction materialelectrically which comprises generating heat on the inner surface of anoutside pipe made of a highly magnetic metal and buried in the inside ofa construction material by passing the alternating current only on theinner surface of the said outside pipe by using a perfectly insulatedwire which is disposed in the inside of the said outside pipe, one endof said insulated wire being connected to the one terminal of analternating current source and the other end connected to the one end ofthe said outside pipe, the other end of the said outside pipe beingdirectly connected to the other terminal of the same alternating currentsource.

2. An apparatus for heating the surface of construction materialelectrically which comprises an outside pipe of highly magnetic metaladapted to be buried in the construction material and a perfectlyinsulated wire disposed in the inside of the said outside pipe, one endof said insulated wire being connected to one terminal of an alternatingcurrent source and the other end connected to a terminal conductivelyfixed on the one end of the said outside pipe, the other end of the saidoutside pipe being directly connected to the other terminal of the saidalternating current source, so as to generate heat only on the innersurface of the said outside pipe when an alternating current is passedthrough the wiring system.

3. An apparatus for heating the surface of construction materialelectrically which comprises an outside pipe of highly magnetic metaladapted to be buried in the construction material and a perfectlyinsulated wire disposed in the inside of the said outside pipe, one endof said insulated wire being connected to one terminal of an alternatingcurrent source and the other end connected to a terminal fixed on oneend of the said outside pipe, the other end of the said outside pipebeing directly connected to the other terminal of the said alternatingcurrent source, so as to generate heat only on the inn-er surface of thesaid outside pipe when an alternating current is passed through thewiring system, the outside surface of said pipe being inter-connected atplaces by steel plates.

References Cited UNITED STATES PATENTS 2,543,882 3/1951 Tice 21910.492,635,168 4/1953 Lerza et a1 21910.49 3,219,800 11/1965 Alexander219-446 RICHARD M. WOOD, Primary Examiner.

L. H. BENDER, Assistant Examiner.

